System for distributed blood flow measurement

Abstract

A medical system for minimally-invasive measurement of blood flow in an artery (AT). An interventional device (IVD) with an optical fiber (FB) comprising a plurality of temperature-sensitive optical sensor segments, e.g. Fiber Bragg Gratings, spatially distributed along its longitudinal extension is configured for insertion into an artery (AT). A temperature changer (TC) is arranged in the WD to introduce a local change in temperature (ΔT) of a bolus of blood in the artery, to allow thermal tracking over time with the optical fiber (FB). A measurement unit (MU) with a laser light source (LS) delivers light to the optical fiber (FB) and receives light reflected from the optical fiber (FB) and generates a corresponding time varying output signal. A first algorithm (A1) translates this time varying output signal into a set of temperatures corresponding to temperatures at respective positions along the optical fiber (FB). A second algorithm (A2) calculates a measure of blood flow (BF) at respective positions along the optical fiber (FB) in accordance with a temporal behavior of said set of temperatures. Such system can be used to quickly scan an artery for diagnosing stenotic regions without the need for pullbacks or injection of toxic liquids. A good spatial resolution of the blood flow measurement can be obtained in real-time.

The invention claimed is: 
     
       1. A medical system for interventional measurement of blood flow in an artery, the medical system comprising:
 an interventional device including an optical fiber having a plurality of temperature-sensitive optical sensor segments spatially distributed along a longitudinal extension of the optical fiber,
 wherein the interventional device is configured for insertion into the artery such that the optical fiber can be positioned inside the artery and be in thermal contact with blood flowing in the artery, and such that the longitudinal extension of the optical fiber follows a longitudinal extension of the artery, and 
 wherein the interventional device further includes a temperature changer configured to introduce a local change in temperature of a bolus of blood in the artery at a position upstream from one end of the optical fiber; 
 
 a measurement unit arranged for operational connection to the interventional device,
 wherein the measurement unit includes a light source for delivering light that is split into a first part of the light and a second part of the light, 
 wherein the first part of the light is delivered to the optical fiber in the interventional device and an interferometer configured to receive light reflected from the plurality of temperature-sensitive optical sensor segments in response to the first part of the light and to generate wavelength data that includes information indicating temperatures at spatial positions of the optical fiber corresponding to the plurality of temperature-sensitive optical sensor segments, and 
 wherein the second part of the light is applied to a wavelength measurement unit configured to monitor wavelength of the light from the light source, the wavelength measurement unit comprising a gas cell with a known optical absorption spectrum and a Mach Zehnder interferometer; and 
 
 a processor unit for operational connection to the measurement unit and a non-transitory storage medium for storing instructions that, when executed by the processor unit, cause the processor unit to:
 spatially and temporally extract the temperatures from the wavelength data into a distributed temperature profile of the temperatures at the respective spatial positions of the plurality of temperature-sensitive optical sensor segments along the optical fiber, the distributed temperature profile being responsive to a downstream flow of the bolus of blood over the plurality of temperature-sensitive optical sensor segments; and 
 
 track local transient changes of temperature at the respective spatial positions of the plurality of temperature-sensitive optical sensor segments along the optical fiber in accordance with the temperatures provided in the distributed temperature profile to detect the blood flow in the artery, wherein
 the local transient changes of temperature are tracked as a function of time for a given position of one of the plurality of temperature-sensitive optical sensor segments along the optical fiber. 
 
 
     
     
       2. The medical system according to  claim 1 ,
 wherein the temperature changer is configured to provide a modulation of cooling or heating of the bolus of blood at a constant frequency, and 
 wherein the measurement unit is configured to measure a spatially distributed temperature of the plurality of temperature-sensitive optical sensor segments at the constant frequency. 
 
     
     
       3. The medical system according to  claim 1 , wherein the temperature changer includes a catheter configured to inject a temporally limited bolus of liquid with a temperature different from a temperature of blood in the artery to introduce the local change in temperature of the bolus of blood in the artery. 
     
     
       4. The medical system according to  claim 1 ,
 wherein the temperature changer includes a temperature changing element arranged for thermal contact with blood in the artery, and 
 wherein the temperature changing element is configured to cool or heat the bolus of blood to introduce the local change in temperature of the bolus of blood in the artery. 
 
     
     
       5. The medical system according to  claim 1 , wherein the plurality of temperature-sensitive optical sensor segments includes at least one of: Fiber Bragg Gratings, or Rayleigh based sensor segments. 
     
     
       6. The medical system according to  claim 1 , wherein the interventional device includes a guidewire in which the optical fiber is arranged. 
     
     
       7. The medical system according to  claim 1 , wherein the light source includes a laser light source configured to provide light at different wavelengths. 
     
     
       8. The medical system according to  claim 1 , wherein spatially and temporally extracting the temperatures from the wavelength data into the distributed temperature profile comprises performing a Fourier analysis of wavelength data associated with each of the temperature-sensitive optical sensor segments. 
     
     
       9. The medical system according to  claim 1 , wherein the interventional device and the measurement unit are arranged for interconnection by means of an optical interface so as to allow the measurement unit and the interventional device to be spatially separated during normal use. 
     
     
       10. The medical system according to  claim 1 , wherein the interventional device is made of non-magnetic materials. 
     
     
       11. A method for minimally-invasive measurement of blood flow in an artery, the method comprising:
 providing an interventional device including an optical fiber having a plurality of temperature-sensitive optical sensor segments spatially distributed along a longitudinal extension of the optical fiber; 
 inserting the interventional device into the artery such that the optical fiber can be positioned inside the artery and be in thermal contact with blood flowing in the artery, and such that the longitudinal extension of the optical fiber follows a longitudinal extension of the artery; 
 introducing a local change in temperature of a bolus of blood in the artery at a position upstream from one end of the optical fiber; 
 splitting light from a light source into a first part of light and a second part; 
 delivering the first part of light to the optical fiber in the interventional device; 
 applying the second part of the light for monitoring wavelength of the light from the light source using a gas cell with a known optical absorption spectrum and a Mach Zehnder interferometer; 
 receiving light reflected from the plurality of temperature-sensitive optical sensor segments in response to the first part of light and generating wavelength data using an interferometer, wherein the wavelength data indicates temperatures at spatial positions of the optical fiber corresponding to the plurality of temperature-sensitive optical sensor segments; 
 spatially and temporally extracting the temperatures from the wavelength data into a distributed temperature profile of the temperatures at the respective positions of the plurality of temperature-sensitive optical sensor segments along the optical fiber, the distributed temperature profile being responsive to a downstream flow of the bolus of blood over the plurality of temperature-sensitive optical sensor segments; and 
 tracking local transient changes of temperature at the respective positions of the plurality of temperature-sensitive optical sensor segments along the optical fiber in accordance with the temperatures provided in the distributed temperature profile to detect the blood flow in the artery, wherein
 the local transient changes of temperature are tracked as a function of time for a given position of one of the plurality of temperature-sensitive optical sensor segments along the optical fiber. 
 
 
     
     
       12. The method according to  claim 11 , wherein introducing the local change in temperature of the bolus of blood in the artery comprises providing a modulation of cooling or heating of the bolus of blood at a constant frequency, wherein the blood flow in the artery is measured at the constant frequency. 
     
     
       13. The method according to  claim 11 , wherein introducing the local change in temperature of the bolus of blood in the artery comprises injecting a temporally limited bolus of liquid with a temperature different from a temperature of blood in the artery through a catheter. 
     
     
       14. The method according to  claim 11 , wherein introducing the local change in temperature of the bolus of blood in the artery comprises cooling or heating the bolus of blood through a temperature changing element in thermal contact with the blood in the artery. 
     
     
       15. The method according to  claim 11 , wherein the plurality of temperature-sensitive optical sensor segments comprise Fiber Bragg Gratings. 
     
     
       16. The method according to  claim 11 , wherein the plurality of temperature-sensitive optical sensor segments comprise Rayleigh based sensor segments.